Construction crew members have signed nondisclosure agreements forbidding them from speaking about their work or photographing or taking video recordings of the site. All materials from the school will be either demolished on site or destroyed elsewhere to ensure none of it is sold or collected. Officials declined to say where the material will be disposed.

“You don’t want to see a brick from Sandy Hook School on eBay,” said Robert Mitchell, chairman of the town’s public building and site commission.

Mr. Mitchell later added: “We still consider it sacred ground.”

Here’s the progress of the demolition as seen in aerial photographs. First is from Dec. 14, 2012, before the process started: